The invention relates to a method of coating a porous substrate with a thin electrolyte layer, particularly a method of coating porous electrodes with thin electrolyte layers. Such electrodes are used mainly in connection with high temperature fuel cells.
DE 44 37 105 and DE 195 20 458 disclose electrode/electrolyte units with thin electrolyte layers of 20 .mu.m which are manufactured by electrophoresis. However, it has been found that, with electrophoresis, only substrates with a certain pore size distribution can be used. Particularly, electrodes which have been made in accordance with the Coat-Mix-process as it is known from DE 33 05 530 and from DE 33 05 529 could not be coated over large areas by the electrophoresis process. The reasons herefor were the large pores which occur in electrodes made by the Coat-Mix process. Electrodes with large pores insure a fast gas exchange in a high temperature fuel cell. It is therefore desirable to maintain a high level of porosity.
It is also known to cast foils for the manufacture of electrolyte layers. For this process, however, large and expensive foil casting tables are required.
It is the object of the present invention to provide a simple coating process by which large-pore substrates can be coated with a thin layer.